Non-planar pMOS structure with a strained channel region and an integrated strained CMOS flow

ABSTRACT

A non-planar tri-gate p-MOS transistor structure with a strained channel region and a non-planar tri-gate integrated strained complimentary metal-oxide-semiconductor (CMOS) structure are described. A relaxed Si 1-x  Ge x  layer is formed on the silicon-on-isolator (SOI) substrate. The relaxed Si 1-x  Ge x  layer is patterned and subsequently etched to form a fin on the oxide. The compressively stressed Si 1-y  Ge y  layer, having the Ge content y higher than the Ge content x in the relaxed Si 1-x Ge x  layer, is epitaxially grown on the fin. The Si 1-y  Ge y  layer covers the top and two sidewalls of the fin. The compressive stress in the Si 1-y  Ge y  layer substantially increases the hole mobility in a channel of the non-planar tri-gate p-MOS transistor structure.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of semiconductor manufacturing, and more specifically, to a semiconductor transistor and its manufacture.

2. Discussion of Related Art

Various techniques are used to improve performance of a metal-oxide-semiconductor (MOS) transistor. Transistors have continuously been scaled down, thus increasing their density, and accordingly, their switching speeds.

Another way to increase the speed of the transistor, is to create a transistor channel with a high mobility of the carriers by, for example, growing a strained silicon (Si) layer on a relaxed silicon germanium (“Si_(1-x) Ge_(x)”) layer thereby increasing mobility of electrons. The tensile strain in the Si layer, however, does not increase the hole mobility. Therefore, for a p-MOS transistor structure, the channel formed from the Si layer under tensile stress cannot provide increased hole mobility. In addition, the tensile strained Si layer is grown on a planar substrate, which limits the density of the transistors and increases intrinsic capacitance.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is described by way of example with reference to the accompanying drawings, wherein:

FIG. 1A is a perspective view of a semiconductor structure having a Silicon-On-Isolator (SOI) substrate for a non-planar strained p-MOS transistor structure fabrication according to one embodiment of the invention;

FIG. 1B is a view similar to FIG. 1A, after a strained Si_(1-x) Ge_(x) layer and an intrinsic Si layer are formed on the SOI substrate;

FIG. 1C is a view similar to FIG. 1B, after annealing to form a relaxed Si_(1-x)Ge_(x) layer;

FIG. 1D is a view similar to FIG. 1C, after forming a tri-gate fin from the relaxed Si_(1-x) Ge_(x) layer according to one embodiment of the invention;

FIG. 1E is a view similar to FIG. 1D, after a strained Si_(1-y) Ge_(y) layer is epitaxially formed on the relaxed Si_(1-x) Ge_(x) tri-gate fin;

FIG. 1F is a cross-sectional view of the semiconductor structure after a high-k dielectric layer is formed on the strained Si_(1-y) Ge_(y) tri-gate fin according to one embodiment of the invention;

FIG. 1G is a cross-sectional view of the semiconductor structure after a tri-gate electrode is formed on the high-k dielectric layer according to one embodiment of the invention;

FIG. 1H is a perspective view of a tri-gate p-MOS semiconductor structure according to one embodiment of the invention;

FIG. 2A is a cross-sectional side view of a semiconductor structure for a non-planar tri-gate CMOS fabrication with tri-gate fins according to one embodiment of the invention;

FIG. 2B is a view similar to FIG. 2A, after covering an n-MOS portion of the semiconductor structure by a protection layer, leaving a p-MOS portion exposed;

FIG. 2C is a view similar to FIG. 2B, after epitaxially forming a strained Si_(1-y) Ge_(y) layer on a tri-gate fin of the p-MOS portion of the semiconductor structure;

FIG. 2D is a view similar to FIG. 2C, after a protection oxide layer is formed on the strained Si_(1-y) Ge_(y) layer covering the tri-gate fin of the p-MOS portion of the semiconductor structure;

FIG. 2E is a view similar to FIG. 2D, after removing the protection layer from the n-MOS portion of the semiconductor structure;

FIG. 2F is a view similar to FIG. 2E, after forming a strained Si layer on a tri-gate fin of the n-MOS portion of the semiconductor structure;

FIG. 2G is a view similar to FIG. 2F, after forming a protection pad oxide layer on the strained Si layer covering the tri-gate fin of the n-MOS portion of the semiconductor structure;

FIG. 2H is a view similar to FIG. 2G, after removing the protection oxide layers from the n-MOS and p-MOS portions of the semiconductor structure;

FIG. 2I is a view similar to FIG. 2H, after forming a high-k dielectric layer on the strained Si layer and Si_(1-y) Ge_(y) layer;

FIG. 2J is a view similar to FIG. 2I, after forming a tri-gate gate electrode on the high-k dielectric layer; and

FIG. 2K is a perspective view of the strained CMOS structure according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

A non-planar strained p-MOS transistor structure and a non-planar integrated strained complementary metal-oxide-semiconductor (CMOS) structure with respective processes of their fabrication are described herein. A relaxed Si_(1-x) Ge_(x) layer is formed on the silicon-on-isolator (SOI) substrate. The relaxed Si_(1-x) Ge_(x) layer is patterned, and subsequently, etched to form a tri-gate fin on the SOI substrate. Further, a Si_(1-y) Ge_(y) layer, having a Ge content y higher than a Ge content x in the relaxed Si_(1-x) Ge_(x) layer, is epitaxially formed on the tri-gate fin formed from the etched relaxed Si_(1-x) Ge_(x) layer on the SOI substrate. The Si_(1-y) Ge_(y) layer covers two opposing sidewalls and a top surface of the tri-gate fin. Due to the higher Ge content, the lattice of the Si_(1-y) Ge_(y) layer has a larger spacing than the spacing of the lattice of the underlying relaxed Si_(1-x) Ge_(x) layer. The larger spacing of the Si_(1-y) Ge_(y) strains the Si_(1-y) Ge_(y) layer, resulting in the compressive stress in the latter. A compressively stressed Si_(1-y) Ge_(y) layer epitaxially grown on the top surface and the two opposing sidewalls of the tri-gate fin formed from the relaxed Si_(1-x) Ge_(x) layer, which rests on the SOI substrate, is used to form a strained channel between a source and drain region of the non-planar p-MOS transistor structure. Compressive stress in Si_(1-y) Ge_(y) layer substantially increases the hole mobility in the transistor channel of the non-planar p-MOS transistor structure improving current-voltage (I-V) characteristics. The I-V characteristics are improved, for example, by increasing a saturation drain current (I_(DSAT)) and a linear drain current (I_(DLIN)) of a non-planar p-MOS transistor, as a result of increased hole mobility in the transistor channel.

FIG. 1A of the accompanying drawings illustrates a semiconductor structure for a non-planar strained p-MOS transistor structure fabrication according to one embodiment of the invention. As shown in FIG. 1A, semiconductor structure 400 includes an insulating layer 402, which is sandwiched between a silicon layer 403 and a bulk monocrystalline silicon substrate 401 forming a silicon-on-isolator (SOI) substrate. Generally, devices are formed in and on the layer of silicon 403. The insulating layer 402 may serve to reduce capacitance between the devices formed in the silicon layer 403 and the substrate 401, resulting in less power consumption and greater circuit speed. In one embodiment, the insulating layer 402 is a buried oxide layer, for example, SiO₂, and the like. In alternative embodiments, the insulating layer 402 may be any one, or a combination of, sapphire, silicon dioxide, silicon nitride, or other insulating materials. The thickness of the silicon layer 403 may be in the approximate range of 2.5 nanometers (“nm”) to 7.5 nm. The thickness of the insulating layer 402 may be in the approximate range of 500 angstroms (“Å”) to 1500 Å. More specifically, the thickness of the silicon layer formed on top surface of the buried oxide layer resting on the monocrystalline Si substrate, is about 5 nm and the thickness of the buried oxide layer is about 1000 Å. The SOI substrate may be formed by any one of the techniques known in the art, for example, separation by implantation of oxygen (SIMOX), hydrogen implantation and separation approach (also called SmartCut®), and the like.

FIG. 1B illustrates a semiconductor structure 400 after a strained Si_(1-x) Ge_(x) layer and an intrinsic Si layer are formed on the SOI substrate. The strained Si_(1-x) Ge_(x) layer 404 and an intrinsic Si layer 405 are subsequently formed on the Si layer 403. The Si_(1-x) Ge_(x) layer 404 is epitaxially grown on the Si layer 403. Generally, Si_(1-x) Ge_(x) material has a lattice structure substantially the same as a monocrystalline Si lattice structure. Because of the presence of Ge atoms, the Si_(1-x) Ge_(x) lattice spacing is substantially larger than the Si lattice spacing. Ge atoms of the Si_(1-x) Ge_(x) layer 404 are diagrammed as large circles, whereas Si atoms are diagrammed as small circles in FIG. 1B. The lattice spacing of the Si_(1-x) Ge_(x) increases with increasing the Ge content x in the Si_(1-x) Ge_(x). The larger lattice spacing strains the Si_(1-x) Ge_(x) layer 404 formed on the Si layer 403 and generates the compressive stress in the Si_(1-x) Ge_(x) layer 404. In one embodiment, an intrinsic Si layer 405 is epitaxially grown on the strained Si_(1-x) Ge_(x) layer 404 to become a capping layer for the Si_(1-x) Ge_(x) layer 404. In one embodiment, the Ge content x in the Si_(1-x) Ge_(x) layer 404 formed on the Si layer 403 is in the approximate range of 0.05 to 0.2 (that is of 5% to 20%). In more specific embodiment, the Ge content x in the Si_(1-x) Ge_(x) layer 404 on the Si layer 403 is about 0.15 that is equivalent to 15%. Generally, the thickness of the strained Si_(1-x) Ge_(x) layer 404 depends on the ultimate device geometry. In one embodiment, to form a non-planar tri-gate transistor structure, the strained Si_(1-x) Ge_(x) layer 404 may have the thickness in the approximate range of 15-25 nm and the intrinsic Si layer 405 may have the thickness in the approximate range between 3 nm to 15 nm. In another embodiment, the strained Si_(1-x) Ge_(x) layer 404 may have the thickness about 20 nm. In yet another embodiment, to form, for example, a double-gate device, the strained Si_(1-x) Ge_(x) layer 404 may be about 100 nm thick.

The heat treatment, or annealing, of the semiconductor structure 400 is carried out to reduce strain of the Si_(1-x) Ge_(x) layer 404. Annealing results in diffusion of the Ge atoms from Si_(1-x) Ge_(x) layer 404 into the underlying Si layer 403 and upper intrinsic Si layer 405, as illustrated in FIG. 1B. The diffusion of the Ge atoms relaxes the strain in the Si_(1-x) Ge_(x) layer 404, such that the relaxed Si_(1-x) Ge_(x) layer 406 is formed, as illustrated in FIG. 1C. In one embodiment, the annealing temperature to relax the strained Si_(1-x) Ge_(x) layer 404 is in the approximate range of 1000 to 1100 C, and more specifically, about 1050 C.

FIG. 1C is a view of the semiconductor structure 400 after annealing. As shown in FIG. 1C, the semiconductor structure 400, after annealing, comprises a relaxed Si_(1-x) Ge_(x) layer 406 formed from the strained Si_(1-x) Ge_(x) layer 404, the Si layer 403 and the intrinsic Si layer 405. The relaxed Si_(1-x) Ge_(x) layer 406 rests on top surface of the buried oxide layer 402 covering the silicon substrate 401. In one embodiment, the total thickness of the relaxed Si_(1-x) Ge_(x) layer 406 may be in the approximate range of 20 nm to 100 nm.

The semiconductor structure 400 is patterned to expose portions of the relaxed Si_(1-x) Ge_(x) layer 406. The exposed portions of the relaxed Si_(1-x) Ge_(x) layer 406 are subsequently etched and removed so that tri-gate fins in the relaxed Si_(1-x) Ge_(x) layer 406 are formed. FIG. 1D shows the semiconductor structure 400 with a tri-gate fin formed from relaxed Si_(1-x) Ge_(x) layer on the oxide layer according to one embodiment of the invention. The tri-gate fin 407 stands above the insulating layer 402, the insulating layer 402 covers the Si substrate 401. In one embodiment, patterning of the relaxed Si_(1-x) Ge_(x) layer 406 to form the tri-gate fin 407 may be performed by using a well known in the art photolithographic technique. Etching the portions of the relaxed Si_(1-x) Ge_(x) layer 406 can be performed with an anisotropic etchant, which selectively removes the exposed portions of the relaxed Si_(1-x) Ge_(x) layer 406 over the other exposed materials of the structure, generating the tri-gate fin 407 with vertical sidewalls. In one embodiment, the width 421 of the tri-gate fin 407 is in the approximate range of 20 nm to 120 nm.

FIG. 1E illustrates a strained Si_(1-y) Ge_(y) 408 selectively grown on the tri-gate fin 407. The strained Si_(1-y) Ge_(y) layer 408 covers the top surface and two opposing sidewalls of the tri-gate fin 407, but does cover the insulating layer 402. Because the Si_(1-y) Ge_(y) layer 408 has the same lattice structure as the relaxed Si_(1-x) Ge_(x) layer 406 comprising the tri-gate fin 407, it can be epitaxially grown on the relaxed Si_(1-x) Ge_(x) layer. In one embodiment, the Si_(1-y) Ge_(y) layer, which is selectively grown by epitaxy on the relaxed Si_(1-x) Ge_(x) tri-gate fin, has the Ge content y approximately from 0.10 to 0.50 (10% to 50%) higher than the Ge content x in the underlying relaxed Si_(1-x) Ge_(x) fin. In another embodiment, the Ge content y of the Si_(1-y) Ge_(y) layer epitaxially grown on the relaxed Si_(1-0.15) Ge_(0.15) tri-gate fin is about 0.3 (30%) higher than the Ge content x in the underlying relaxed Si_(1-x) Ge_(x) fin. In yet another embodiment, the Ge content y of the Si_(1-y) Ge_(y) layer epitaxially grown on the relaxed Si_(1-0.15) Ge_(0.15) tri-gate fin is about 0.3 (30%). Generally, the higher Ge content means larger lattice spacing of the Si_(1-y) Ge_(y) layer relative to the relaxed Si_(1-x) Ge_(x) layer. Larger lattice spacing creates compressive stress in the Si_(1-y) Ge_(y) layer covering the top surface and two opposing sidewalls of the relaxed Si_(1-x) Ge_(x) tri-gate fin. The compressive stress in the Si_(1-y) Ge_(y) layer reduces the effective mass of the p-type carriers (holes) that substantially increases the hole mobility in a channel of the non-planar PMOS transistor, wherein the channel is formed in the strained Si_(1-y) Ge_(y) layer 408. In one embodiment, the hole mobility enhancement factor in the channel formed in the strained Si_(1-y) Ge_(y) layer 408 is in the approximate range of 1.2 to 5.

In one embodiment, the strained Si_(1-y) Ge_(y) layer 408 may be epitaxially grown on the tri-gate fin 407 by a low pressure chemical vapour deposition (CVD) technique including Silane (SiH4) and Germane (GeH₄) gases. For another embodiment, the strained Si_(1-y) Ge_(y) layer 408 may be epitaxially grown on the relaxed Si_(1-x) Ge_(x) tri-gate fin 407 by a low pressure chemical vapour deposition (CVD) technique including DichloroSilane (SiCl₂H₂) and Germane (GeH₄) gases. In one embodiment, the pressure in the reactor may be in the approximate range of 1 torr to 400 torr and the temperature may be in the approximate range of 300 C to 900 C. In one embodiment, the thickness of the strained Si_(1-y) Ge_(y) layer selectively grown by epitaxy on the relaxed Si_(1-x) Ge_(x) tri-gate fin is in the approximate range of 50 Å to 200 Å. More specifically, the thickness of the strained Si_(1-y) Ge_(y) layer is about 100 Å. Further, a n-type dopant, for example, arsenic (“As”), phosphorus (“P”), and the like, is added to the relaxed Si_(1-x) Ge_(x) tri-gate fin 407 covered by the strained Si_(1-y) Ge_(y) layer 408 to form a n-well. The n-type dopant may be added by using, for example, the ion implantation technique. The concentration of the n-type dopants is in the approximate range of 2×10¹⁶ cm⁻³ to 2×10¹⁹ cm⁻³.

As illustrated in FIG. 1F, a dielectric layer is formed on the strained Si_(1-y) Ge_(y) layer. The dielectric layer 409 covers the top surface and two opposing sidewalls of the tri-gate fin 407 with the strained Si_(1-y) Ge_(y) layer 408. The dielectric layer 409 forms a gate dielectric of the tri-gate transistor structure. In one embodiment, the dielectric layer 409 may be blanket deposited, patterned, and etched into the gate dielectric utilizing known photolithographic and etching techniques. In one embodiment, the dielectric layer may include oxide of a transition metal. In one embodiment, the dielectric layer 409 may include a high-k dielectric, for example, zirconium oxide(“ZrO₂”). For alternative embodiments, the dielectric layer 409 may include of any one of a hafnium oxide(“HFO₂”) and lanthanum oxide (“La₂O₄”). The thickness of the dielectric layer 409 may be between 10 Å and 40 Å.

FIG. 1G is a cross-sectional view of the semiconductor structure 400 after a tri-gate electrode layer is formed on the high-k dielectric layer according to one embodiment of the invention. The tri-gate electrode layer 411 is formed on the dielectric layer 409 covering the top surface and the sidewalls of the tri-gate fin 407, as illustrated in FIG. 1G. In one embodiment, the thickness of the tri-gate electrode layer 411 is in the approximate range of 500 Å to 1500 Å. In one embodiment, the tri-gate electrode layer 411 may be formed by blanket deposition of polysilicon and patterning the polysilicon into the tri-gate electrode utilizing known photolithographic techniques. For an embodiment, the tri-gate electrode layer 411 and the underlying dielectric layer 409 may be subsequently patterned and etched to a predetermined width. In another embodiment, the tri-gate electrode layer 411 includes a metal underlayer under the polysilicon. In yet another embodiment, the tri-gate electrode layer 411 is a metal.

FIG. 1H is a perspective view of a tri-gate p-MOS semiconductor structure 400 according to one embodiment of the invention. The structure 400 has a source region 413 and a drain region 414 formed in the fin structure (“fin body”) 418 at opposite sides of the gate electrode 421. The gate electrode 421 with underlying dielectric 429 has a predetermined width 415 and covers a portion of the fin body 418. For an embodiment, the fin body 418 includes a tri-gate fin 407 formed from relaxed Si_(1-x) Ge_(x) layer covered by the strained Si_(1-y) Ge_(y) layer 408. The fin body 418 is formed on top surface of the insulating layer 402. The insulating layer 402 rests on the silicon substrate 401. In one embodiment, the width 415 of the gate electrode 421 is in the approximate range of 80 nm to 120 nm, the thickness 416 of the fin body 418 is in the approximate range of 20 nm to 120 nm, and the width 417 of the fin body 418 is in the approximate range of 20 nm to 120 nm. For an embodiment, to form the source region 413 and the drain region 414 of the p-MOS transistor structure 400, a p-type dopant, for example, boron (“B”) is added to the fin body 418 at the opposite sides of the gate electrode 421, for example, by ion implantation. For an embodiment, the concentration of the p-type dopants is in the approximate range of 10¹⁸ cm⁻³ to 10²¹ cm⁻³.

FIGS. 2A-2K illustrate an exemplary process to fabricate a strained non-planar tri-gate CMOS structure, according to one embodiment of the invention. FIG. 2A illustrates a cross-sectional view of the semiconductor structure 500 for tri-gate CMOS fabrication with two tri-gate fins 503N and 503P formed from a relaxed Si_(1-x) Ge_(x) layer. As shown in FIG. 2A, the tri-gate fins 503N and 503P formed from a relaxed Si_(1-x) Ge_(x) layer are located on an oxide layer 502, which covers a Si substrate 501. One of the tri-gate fins 503N belongs to an n-MOS portion 520 of the semiconductor structure, whereas the other tri-gate fin 503P belongs to a p-MOS portion 530 of the CMOS structure. Semiconductor structure 500 having tri-gate fins 503N and 503P formed from the relaxed Si_(1-x) Ge_(x) layer may be fabricated using the process described presently. Next, before forming the p-MOS portion 530, the n-MOS portion 520 is covered by a first protection layer to protect the n-MOS portion during p-MOS portion formation.

FIG. 2B is a cross-sectional view of the semiconductor structure 500 after covering the n-MOS portion by a first protection layer. The p-MOS portion 530 of the structure 500 is uncovered, while the first protection layer 505 covers the top surface and sidewalls of the tri-gate fin 503N that belongs to the n-MOS portion 520. For an embodiment, the first protection layer 505 may be formed, for example, by depositing a silicon nitride (“Si₃N₄”) layer on the wafer, forming a resist on the Si₃N₄ layer, patterning the resist to expose portions of the Si₃N₄ layer covering the p-MOS portion 530, etching the silicon nitride layer on the p-MOS portion 530 to expose p-MOS portion 530, and then ashing the resist producing the structure in FIG. 2B. In alternative embodiments, other implant mask materials may be used as a first protection layer 505. Next, to form a strained channel in the p-MOS portion 530 of the semiconductor structure 500, a strained Si_(1-y) Ge_(y) layer is selectively formed on the tri-gate fin 503P of the p-MOS portion 530.

FIG. 2C shows a cross-sectional view of the semiconductor structure 500 after epitaxially forming a strained Si_(1-y) Ge_(y) layer on the tri-gate fin of the p-MOS portion. The n-MOS portion 520 is covered by the first protection layer 505. The strained Si_(1-y) Ge_(y) layer 504 covers the top surface and two opposing sidewalls of the tri-gate fin 503P of the p-MOS portion 530 of the structure 500 leaving the oxide layer 502 uncovered. In one embodiment, the strained Si_(1-y) Ge_(y) layer 504 is selectively epitaxially grown on the top surface and two opposing sidewalls of the tri-gate fin 503P of the p-MOS portion 530. More specifically, the strained Si_(1-y) Ge_(y) layer 504 is grown by low pressure CVD technique with a flow including SiH₄ and GeH₄ gases. For another embodiment, the strained Si_(1-y) Ge_(y) layer 504 may be epitaxially grown by a low-pressure chemical vapour CVD with a flow including of SiCl₂H₂ and GeH₄ gases. The pressure in the reactor may be in the approximate range of 1 torr to 400 torr and the temperature may be in the approximate range of 300 C to 900 C.

The strained Si_(1-y) Ge_(y) layer 504 has a Ge content y approximately 15% higher than the Ge content x of the relaxed Si_(1-x) Ge_(x) layer of the tri-gate fin 503P and a lattice spacing substantially larger than the lattice spacing of the Si_(1-x) Ge_(x) layer of the tri-gate fin 503P that results in a compressive stress in the strained Si_(1-y) Ge_(y) layer 504 along the top surface and two opposing sidewalls of the tri-gate fin 503P of the p-MOS portion 530. In one embodiment, the strained Si_(1-y) Ge_(y) layer 504 has the Ge content y about 10% to 50% higher than the relaxed Si_(1-x) Ge_(x) layer of the tri-gate fin 503P. In one embodiment, the strained Si_(1-y) Ge_(y) layer 504 has the Ge content y about 0.3 (30%) and the relaxed Si_(1-x) Ge_(x) layer of the tri-gate fin 503P has the Ge content x of about 0.15 (15%). The compressive stress increases the hole mobility in the strained Si_(1-y) Ge_(y) layer 504. In one embodiment, the hole mobility enhancement factor in the channel formed in the strained Si_(1-y) Ge_(y) layer 408 is in the approximate range of 1.2 to 5. In one embodiment, the thickness of the strained Si_(1-y) Ge_(y) layer 504 is in the approximate range of 50 Å to 200 Å, and more specifically, about 100 Å. Further, to form a n-well, a n-type dopant is added to the tri-gate fin 503N covered by the strained Si_(1-y) Ge_(y) layer 504. The n-type dopant may be any one of As, P, and the like. The n-type dopant may be added, for example, by the ion implantation technique. For an embodiment, the concentration of the dopants is in the approximate range of 2×10¹⁷ cm⁻³ to 2×10¹⁹ cm⁻³. In one embodiment, before the ion implantation, the strained Si_(1-y) Ge_(y) layer 504 may be covered by a second protection layer to protect the surface of the strained Si_(1-y) Ge_(y) layer 504 from unnecessary damage.

FIG. 2D is a cross-sectional view of the semiconductor structure 500 having a second protection layer 506 formed on the strained Si_(1-y) Ge_(y) layer. The second protection layer 506 is deposited on the strained Si_(1-y) Ge_(y) layer 504 along the top surface and two opposing sidewalls of the tri-gate fin 503P of the p-MOS portion 530. For an embodiment, the second protection layer 506 may be a silicon oxide layer formed by the epitaxial growth and the subsequent oxidation of silicon. For another embodiment, the second protection layer 506 may be a second silicon nitride layer formed by patterning and etching technique, which is known to one of ordinary skill in the art of semiconductor fabrication. For example, the protection layer 506 may be formed by repeating the deposition of silicon nitride layer on the wafer, lithographically patterning the silicon nitride layer to leave a resist on the p-MOS portion 530, etching the silicon nitride layer off the n-MOS portion 520, and then stripping off the resist.

The second protection layer 506 also protects the p-MOS portion 530 from, for example, unnecessary deposition of Si during the strained channel formation at the n-MOS portion 520 of the semiconductor structure 500. The thickness of the second protection layer 506 may be in the approximate range of 30 Å to 100 Å. Next, to form a n-MOS portion, the first protection layer 505 is removed from the n-MOS portion 520 of the semiconductor structure 500.

FIG. 2E is a cross-sectional view of the semiconductor structure 500, after removing the first protection layer 505 from the n-MOS portion of the semiconductor structure 500. For an embodiment, the first protection layer 505 may be removed by, for example, wet etching using a hot phosphoric acid. Further, to form a strained channel, the strained Si layer is epitaxially grown on the tri-gate fin 503N of the n-MOS portion 520.

FIG. 2F is a cross-sectional view of the semiconductor structure after forming a strained Si layer on the tri-gate fin of the n-MOS portion. The strained Si layer 507 covers the top surface and two opposing sidewalls of the fin tri-gate 503N of the n-MOS portion 520 of the semiconductor structure 500 and does not cover the oxide layer 502. For an embodiment, the strained Si layer 507 may be formed by the epitaxy. Because of presence of Ge atoms, the Si_(1-x) Ge_(x) layer of the tri-gate fin 503N has substantially larger lattice spacing, than the lattice spacing of the Si layer, resulting in a tensile strain in the Si layer along the top surface and two opposing sidewalls of the tri-gate fin 503N of the n-MOS portion 520. The tensile strain increases the electron mobility in the strained Si layer 507 of the n-MOS portion 520 of the semiconductor structure 500. In one embodiment, the electron mobility enhancement factor in the channel formed in the strained Si layer 507 is in the approximate range of 1.2 to 5. In one embodiment, the thickness of the strained Si layer 507 is in the approximate range of 50 Å to 200 Å, and more specifically, about 100 Å.

Further, a p-well is formed in the n-MOS portion 520. For an embodiment, to form a p-well, a p-type dopant, for example, B, and the like, is added to the tri-gate fin 503N covered by the strained Si layer 507 by the ion implantation technique. For an embodiment, before the ion implantation, to protect the surface of the channel during the ion implantation, the pad oxide layer is formed on the strained Si layer, covering the top surface and two opposing sidewalls of the tri-gate fin 503N. The concentration of p-dopants is in the approximate range of 2×10¹⁷ cm⁻³ to 2×10¹⁹ cm⁻³.

FIG. 2G is a cross-sectional view of the semiconductor structure 500 after forming a pad oxide layer. The pad oxide layer 508 is formed on the strained Si layer 507 covering the tri-gate fin 503N of the n-MOS portion 530. The pad oxide layer 508 covers the strained Si layer 507 along the top surface and two opposing sidewalls of the tri-gate fin 503N. In one embodiment, the pad oxide layer 508 is a silicon oxide. Next, the second protection layer 506 and the pad oxide layer 508 are removed from the n-MOS portion 520 and the p-MOS 530 portion, respectively.

FIG. 2H is a cross-sectional view of the semiconductor structure 500 after removing the oxide layers from the n-MOS and p-MOS portions. In one embodiment, the second protection layer 506 and the pad oxide layer 508 may be removed by, for example, wet etching. Next, a dielectric layer is formed on the strained Si and Si_(1-y) Ge_(y) layers.

FIG. 2I is a cross-sectional view of semiconductor structure 500 after forming a dielectric layer on the strained Si layer and Si_(1-y) Ge_(y) layer, which respectively covers the tri-gate fins of each of the n-MOS and p-MOS portions. The dielectric layer 509 is deposited on the strained Si layer 507 and the strained Si_(1-y) Ge_(y) layer 504, covering the top surface and two opposing sidewalls of the tri-gate fins 503N and 503P of the n-MOS portion 520 and the p-MOS 530 portion respectively, as illustrated in FIG. 21. In one embodiment, the dielectric layer 509 may be blanket deposited, patterned, and etched into the gate dielectric using known photolithographic and etching techniques. For an embodiment, the dielectric layer 509 is a high-k dielectric. For an embodiment, the dielectric layer 509 may include an oxide For another embodiment, the dielectric layer 509 may include an oxide of transition metal. For alternative embodiments, the dielectric layer 509 may be made of ZrO₂, HFO₂, or La₂O₅ or any combination thereof. For an embodiment, the dielectric layer 509 may be formed to the thickness in the approximate range of 10 Å to 40 Å. Next, the tri-gate electrode layer is formed on the dielectric layer 509.

FIG. 2J is a cross-sectional view of the semiconductor structure 500, after forming a tri-gate electrode layer. The tri-gate electrode layer 510 is formed on the gate dielectric layer 509 covering the top surface and two opposing sidewalls of each of the tri-gate fins 503N and 503P of the n-MOS 520 portion and the p-MOS portion 530. For an embodiment, the thickness of the tri-gate electrode layer 510 is in the approximate range of 500 Å to 1500 Å. For an embodiment, the tri-gate electrode layer 510 may be formed by blanket deposition of polysilicon. Then, the tri-gate electrode layer 510 may be patterned and etched into the tri-gate electrode using known in the art photolithographic and etching techniques. For an embodiment, the tri-gate electrode layer 510 with the underlying dielectric layer 509 are patterned and etched to a predetermined width.

FIG. 2K is a perspective view of the non-planar tri-gate CMOS structure 600 according to one embodiment of the invention. The CMOS structure 600 has the n-MOS portion 520 and the p-MOS portion 530. The n-MOS portion 520 has a source region 523 and a drain region 524 formed in the portions of n-MOS fin structure (“n-MOS fin body”) 525 at opposite sides of the gate electrode 521. The n-MOS gate electrode 521 with the underlying dielectric layer 509 has the width 542 and covers the top surface and two opposing sidewalls of the n-MOS fin body 525. The n-MOS fin body 525 is formed on top surface of the oxide layer 502. The oxide layer 502 covers the silicon substrate 501. For an embodiment, the n-MOS fin body 525 includes a relaxed Si_(1-x) Ge_(x) layer covered by the tensile strained Si layer. A strained channel of the n-MOS portion 527 is formed in the tensile strained Si layer under the dielectric layer 509 along the top surface and the two opposing sidewalls of the fin body 525. For an embodiment, to form the source region 523 and the drain region 524 of the n-MOS portion of the CMOS structure, a n-type dopant, for example, arsenic (“As”) is added into the fin body 525 on the opposite sides of the gate electrode 521 on the n-MOS portion 520 of the CMOS structure 600. The n-type dopant may be added by, for example, the ion implantation. For an embodiment, the concentration of n-dopants maybe in the approximate range of 10¹⁸ cm⁻³ to 10²¹ cm⁻³.

The p-MOS portion 530 has a source region 533 and a drain region 534 formed in the p-MOS fin body 535 on opposite sides of the gate electrode 531. The p-MOS gate electrode 531 with underlying dielectric layer 509 has the predetermined width 542 and covers the top surface and the two opposing sidewalls of the p-MOS fin body 535. The p-MOS fin body 535 is formed on top surface of the oxide layer 502. The oxide layer 502 covers the silicon substrate 501. For an embodiment, the p-MOS fin body 535 of the p-MOS portion includes the relaxed Si_(1-x) Ge_(x) layer, wherein the top surface and two opposing sidewalls of the relaxed Si_(1-x) Ge_(x) layer are covered by the compressively strained Si_(1-y) Ge_(y) layer. A strained channel 537 of the p-MOS portion 530 is formed in the compressively strained Si_(1-y) Ge_(y) layer under the gate dielectric layer 509 along the top surface and the two opposing sidewalls of the p-MOS fin body 535. For an embodiment, to form the p-MOS source region 533 and the p-MOS drain region 534 of the CMOS structure 600, a p-type dopant, for example, boron (“B”) is added into the p-MOS fin body 535 at the opposite sides of the gate electrode 531 on the p-MOS portion 530 of the CMOS structure 600. The p-type dopant may be added by, for example, the ion implantation. For an embodiment, the concentration of p-dopants may be in the approximate range of 10¹⁸ cm⁻³ to 10²¹ cm⁻³.

For an embodiment, the width 542 of the n-MOS tri-gate electrode 521 and the p-MOS tri-gate electrode 531 with the underlying dielectric 509 may be in the approximate range of 30 nm to 120 nm each. The width 541 of the n-MOS fin body 525 and the p-MOS fin body 535 may be in the approximate range of 30 nm to 120 nm each. The thickness 543 of the n-MOS fin body 525 and the p-MOS fin body 535 may be in the approximate range of 20 nm to 120 nm each.

While certain exemplary embodiments have been described and shown in the accompanying drawings, it is to be understood that such embodiments are merely illustrative and not restrictive of the current invention, and that this invention is not restricted to the specific constructions and arrangements shown and described since modifications may occur to those ordinarily skilled in the art. It may, for example, be possible to create similar structures utilizing materials other than Si and SiGe. 

1. A method of forming a semiconductor structure, comprising: forming an insulating layer; forming a first layer that includes a first germanium content on the insulating layer, the first layer having a first lattice spacing, wherein the forming the first layer comprises forming a third layer having a third germanium content over the insulating layer, and forming a silicon layer on the third layer; forming a fin having a top surface and opposing sidewalls from the first layer; and forming a second layer that includes a second germanium content on the fin, wherein the second layer covers the top surface and the opposing sidewalls of the fin and has a second lattice spacing, which is larger than the first lattice spacing.
 2. The method of claim 1, further comprising: forming a gate dielectric layer on the second layer; forming a gate electrode on the gate dielectric layer; and forming a source region and a drain region on opposing sides of the gate electrode.
 3. The method of claim 1, wherein forming the second layer on the fin comprises an epitaxial growth.
 4. The method of claim 1, wherein the second layer covering the fin is under compressive stress.
 5. The method of claim 1, wherein the first layer is a relaxed SiGe layer and the second layer is a compressively strained SiGe layer.
 6. A method of forming a semiconductor transistor structure, comprising: forming a first layer that includes a first germanium content on an insulating layer on a substrate, the first layer having a first lattice spacing, wherein the forming the first layer comprises forming a third layer having a third germanium content over the insulating layer, and forming a silicon layer on the third layer; forming a first and a second fin from the first layer, the first fin being on a first portion and the second fin being on a second portion of a semiconductor transistor structure; protecting a first portion of the semiconductor transistor structure with a first protective layer; forming a second layer that includes a second germanium content having a second lattice spacing substantially larger than the first lattice spacing on the second fin; removing the first protective layer from the first portion of the semiconductor transistor structure and protecting the second portion of the semiconductor transistor structure with a second protective layer; and forming a fourth layer of a third material having a third lattice spacing substantially smaller than the first lattice spacing on the first fin.
 7. The method of claim 6, further comprising: forming gate dielectrics on the second layer and on the fourth layer of the third material; forming gate electrodes on each of the gate dielectrics; and forming a source region and a drain region at opposing sides of each of the first and the second gate electrodes.
 8. The method of claim 6, wherein the second layer comprises silicon germanium and the third material comprises silicon.
 9. The method of claim 6, wherein forming the second layer and the fourth layer comprises epitaxial growth.
 10. The method of claim 9, wherein the second layer covers a top and two opposing sidewalls of the second fin and the fourth layer covers a top and two opposing sidewalls of the first fin. 